紫外光通信中副载波强度调制的低密度奇偶校验码研究
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摘要
在紫外光散射通信系统中,脉冲展宽和噪声会对信号产生严重影响。为降低系统误码率、提高通信距离,加入了低密度奇偶校验码(LDPC)进行码元纠错。对比了开关键控(OOK)和二进制相移键控(BPSK)副载波强度调制的性能,仿真分析了BPSK副载波强度调制下不同编码效率、不同译码方式的LDPC码对非直视(NLOS)紫外光通信系统误码率的影响。结果表明:BPSK副载波强度调制的性能优于OOK调制,编码效率越小的LDPC码的纠错能力越强,置信传播算法和对数似然比置信传播算法译码性能几乎一致,均优于最小和算法。在小角度、短距离时,非直视紫外光通信系统误码率更小,当误码率为6.5×10-6时,LDPC(672,168)码与未编码序列相比,通信距离提高约一倍。
In ultraviolet(UV)scattering communication systems,pulse broadening and noise considerably affect the signal.To reduce system bit error rate and increase communication distance,it is necessary to add low-density parity check code(LDPC)to implement symbol error correction.The performance of on-off keying(OOK)modulation and binary phase-shift keying(BPSK)for subcarrier intensity modulation is compared.Further,the influence of LDPC codes with different coding efficiencies and decoding methods under BPSK subcarrier intensity modulation on the bit error rate of a non-line-of-sight(NLOS)ultraviolet communication system is simulated and analyzed.Results indicate that BPSK subcarrier intensity modulation performs better than OOK modulation.LDPC codes with low coding efficiency values exhibit strong error correction ability.The performances of belief propagation(BP)algorithms and log-likelihood ratio belief propagation(LLR BP)algorithms are virtually the same,and both are better than min-sum algorithms.When the bit error rate is 6.5 × 10-6,the communication distance of the LDPC(672,168)coded sequence is approximately doubled,compared with the uncoded sequence.
In ultraviolet(UV)scattering communication systems,pulse broadening and noise considerably affect the signal.To reduce system bit error rate and increase communication distance,it is necessary to add low-density parity check code(LDPC)to implement symbol error correction.The performance of on-off keying(OOK)modulation and binary phase-shift keying(BPSK)for subcarrier intensity modulation is compared.Further,the influence of LDPC codes with different coding efficiencies and decoding methods under BPSK subcarrier intensity modulation on the bit error rate of a non-line-of-sight(NLOS)ultraviolet communication system is simulated and analyzed.Results indicate that BPSK subcarrier intensity modulation performs better than OOK modulation.LDPC codes with low coding efficiency values exhibit strong error correction ability.The performances of belief propagation(BP)algorithms and log-likelihood ratio belief propagation(LLR BP)algorithms are virtually the same,and both are better than min-sum algorithms.When the bit error rate is 6.5 × 10-6,the communication distance of the LDPC(672,168)coded sequence is approximately doubled,compared with the uncoded sequence.
引文
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[2]Li H T,Li X Y,Ye Y Z,et al.Ultraviolet communication and its military application prospects[J].Information&Communications,2016(12):60-62,66.李海涛,李晓毅,叶永桢,等.紫外光通信及其军事应用前景[J].信息通信,2016(12):60-62,66.
[3]Song P,Zhou X L,Zhao T F,et al.Node design and analysis of communication performance between nodes in ultraviolet mobile ad hoc networks[J].Acta Optica Sinica,2018,38(3):0306004.宋鹏,周显礼,赵太飞,等.紫外光移动自组网节点设计及通信性能分析[J].光学学报,2018,38(3):0306004.
[4]Song X M,Song F,Song P,et al.Routing protocol of ultraviolet space division multiplexing ad hoc network[J].Chinese Journal of Lasers,2017,44(10):1006005.宋晓梅,宋菲,宋鹏,等.紫外光空分复用自组织网络路由协议[J].中国激光,2017,44(10):1006005.
[5]Qiang R X,Zhao S H,Liu Y.Influence of pulse broadening on bit error rate of ultraviolet communication[J].Laser&Infrared,2015,45(5):559-563.强若馨,赵尚弘,刘韵.脉冲展宽对紫外光通信误码率的影响[J].激光与红外,2015,45(5):559-563.
[6]Liu W K,Zhang F,Wu M L,et al.Research on LDPC coding in ultraviolet communication systems and its implementation[J].Study on Optical Communications,2014,40(5):63-65.刘文楷,张锋,武梦龙,等.LDPC码在紫外光通信中的研究实现[J].光通信研究,2014,40(5):63-65.
[7]Gallager R.Low-density parity-check codes[J].IRETransactions on information theory,1962,8(1):21-28.
[8]Wu M L,Han D H,Zhang X,et al.Experimental research and comparison of LDPC and RS channel coding in ultraviolet communication systems[J].Optics Express,2014,22(5):5422-5430.
[9]Popoola W O,Ghassemlooy Z.BPSK subcarrier intensity modulated free-space opticalcommunications in atmospheric turbulence[J].Journal of Lightwave Technology,2009,27(8):967-973.
[10]Wang Y,Gu S.Ultraviolet communication system based on BPSK subcarrier intensity modulation[J].Proceedings of SPIE,2015,9446:94461K.
[11]Reilly D M,Warde C.Temporal characteristics of single-scatter radiation[J].Journal of the Optical Society of America,1979,69(3):464-470.
[12]Li B F,Wang H X,Liu M,et al.Applicability of non-line-of-sight ultraviolet single-scatter approximation model[J].Photonic Network Communications,2016,31(1):147-154.
[13]Han D H,Fan X,Zhang K,et al.Research on multiple-scattering channel with Monte Carlo model in UV atmosphere communication[J].Applied Optics,2013,52(22):5516-5522.
[14]Wang X F,Zhang X,Zhang J Z,et al.Ultraviolet light atmospheric scattering propagation model based on Monte Carlo method[J].Laser&Optoelectronics Progress,2017,54(11):110102.王晓芳,张新,张继真,等.基于蒙特卡罗方法的紫外光大气散射传输模型[J].激光与光电子学进展,2017,54(11):110102.
[15]Song P,Ke X Z,Xiong Y Y,et al.Pulse broadening effect of non-line-of-sight ultraviolet in noncoplanar communication system[J].Acta Optica Sinica,2016,36(11):1106004.宋鹏,柯熙政,熊扬宇,等.非直视紫外光在非共面通信系统中的脉冲展宽效应[J].光学学报,2016,36(11):1106004.
[16]Hou W J,Liu C H,Lu F P,et al.Non-line-of-sight ultraviolet single-scatter path loss model[J].Photonic Network Communications,2018,35(2):251-257.
[17]Wang P,Zhang H M,Xu Z Y.Simplified model and experimental validation for ultraviolet singlescattering channels[J].Chinese Optics Letters,2015,13(8):080603.
[18]Luettgen M R,Reilly D M,Shapiro J H.Non-lineof-sight single-scatter propagation model[J].Journal of the Optical Society of America A,1991,8(12):1964-1972.
[19]Luo C,Li J Y,Chen X M.Analysis of channel of wireless ultraviolet communication[J].Laser&Optoelectronics Progress,2011,48(4):040602.罗畅,李霁野,陈晓敏.无线紫外通信信道分析[J].激光与光电子学进展,2011,48(4):040602.
[20]Liu B,Tong S,Bai B M.Algebraic construction of low-density parity-check codes without short cycles[J].Journal of Electronics&Information Technology,2004,26(11):1778-1782.刘斌,童胜,白宝明.不含小环的低密度校验码的代数构造方法[J].电子与信息学报,2004,26(11):1778-1782.